Self-adjusting liner for centrifugal pump

ABSTRACT

A self-adjusting liner assembly for installation within a centrifugal pump of the type having an impeller and a pump casing having a suction inlet is provided, comprising a liner having a sealing end, the sealing end having at least one substantially planar outer most surface for contacting an outer surface of the impeller; and a resilient member disposed in the liner, said resilient member providing a force so that the at least one outer most surface remains in substantially continuous contact with the outer surface of the impeller.

FIELD OF THE INVENTION

The present invention relates to centrifugal pumps in general and morespecifically to a self-adjusting liner assembly for centrifugal pumpsfor substantially reducing recirculation damage to the impeller.

BACKGROUND OF THE INVENTION

Centrifugal pumps are commonly used to move mixtures of solids andliquids through piping. The mixture enters the pump impeller along ornear the rotating axis and is accelerated by the impeller, flowingradially outward into a diffuser or volute (casing) which surrounds theimpeller from where it exits into the downstream piping.

Most centrifugal pumps which handle mineral slurries, for example, oilsand slurries, run into problems with respect to solid particles of theslurry becoming trapped between the rotating impeller and thesurrounding volute during operation, thereby causing wear and abrasionof both the impeller and the volute. This results in downtimes forrepair and ultimately reduces the life of the pump and its hydraulicefficiency. The problem tends to be more serious on the suction side ofthe impeller, where the high pressure liquid inside the dischargeportion of the volute tends to flow towards the low pressure zone in thesuction portion of the pump. This is commonly referred to assuction-side recirculation, which results in a loss of pump hydraulicperformance and efficiency.

In particular, increase in suction-side recirculation may directlycontribute to loss of efficiency. Since efficiency is a ratio of outputwork against input power, and since output work (flow and head) is lesswith the same amount of input power, efficiency is lower. Furthermore,as wear increases, the gap between the impeller and the volute becomeslarger if unaddressed and a higher rate of flow can pass through thegap, speeding the deterioration process. Thus, the pump life span willbe reduced.

Many centrifugal slurry pumps are now equipped with an annular suctionliner (also referred to as an annular wear ring), which is locatedbetween the suction side of the impeller and the volute to decrease thewear due to recirculation. However, these suction liners still create agap where solids can cause abrasion damage. Furthermore, the entireoperation (e.g., pumps) must be stopped in order to replace the suctionliner when it has become sufficiently worn. Also, it is somewhatunpredictable as to when the suction liner will need to be replaced,which may result in unexpected pump failures.

In an attempt to at least partially remedy some of the problemsencountered above, CA 2,214,415 and U.S. Pat. No. 5,921,748 teach a wearring which is axially adjustable by means of one or more adjustmentscrews. The adjustment screws are located outside of the pump and, thus,the wear ring (suction liner) can be adjusted while the pump is inoperation. However, one will still have to rely on human intervention toadjust the wear ring according to a schedule or a particular criterion.Furthermore, in between these adjustments, wear will occur, allowing acontinuing increase in recirculation.

U.S. Pat. No. 7,189,054 teaches a wear ring which is axiallyself-adjusting by means of balanced flush water pressures. However, inthis design, physical contact between the wear ring and the impeller isexpressly avoided. When pressurized water is applied to the water inletend of the seal, the seal will move to a self-compensating balancebetween the pump casing and the impeller of the pump. Therefore, theseal cannot be independently adjusted.

It would be desirable to have a suction liner assembly which wouldautomatically adjust according to the wear thereon so that a proper sealbetween the suction side of the impeller and the volute can always bemaintained, resulting in substantially reduced suction-siderecirculation for longer periods of time. While the design in U.S. Pat.No. 7,189,054 has this feature, the driving force to create theadjustment is limited by the use of balanced hydraulic forces to locatethe adjustable component. If, as seems likely, solid material were toaccumulate in the gaps on either side of the adjustable component, thehydraulic force required to advance towards the impeller may not besufficient to overcome the friction due to solids accumulation; theadjustment mechanism seems vulnerable to loss of function.

SUMMARY OF THE INVENTION

The present invention relates to centrifugal pumps in general and morespecifically to a self-adjusting liner assembly for a centrifugal pump.

In one aspect of the present invention, a self-adjusting liner assemblyfor installation within a centrifugal pump of the type having animpeller and a pump casing having a suction inlet is provided,comprising:

-   -   a liner having a sealing end, the sealing end having at least        one substantially planar outer most surface for contacting an        outer surface of the impeller; and    -   a resilient member disposed in the liner, said resilient member        providing a force so that the at least one outer most surface        remains in substantially continuous contact with the outer        surface of the impeller.

In one embodiment, the at least one outer most surface comprises a wearring. In another embodiment, the liner includes a recessed portion forhousing the resilient member and the wear ring. The wear ring may varyin diameter relative to the liner and, in one embodiment, may have anouter diameter essentially the same as the outer diameter of the lineritself.

In one embodiment, the resilient member is a spring such as a wavespring.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings wherein like reference numerals indicatesimilar parts throughout the several views, several aspects of thepresent invention are illustrated by way of example, and not by way oflimitation, in detail in the figures, wherein:

FIG. 1 is a cross-sectional view of the interior of a conventionalsingle stage centrifugal pump.

FIG. 2 is a cross-sectional view of the interior of a single stagecentrifugal pump having an embodiment of a self-adjusting liner assemblyof the present invention.

FIG. 3 is a cross-sectional view of an embodiment of a self-adjustingliner assembly of the present invention prior to wear of the liner.

FIG. 4 is an isometric exploded view of the embodiment of theself-adjusting liner assembly of FIG. 3.

FIG. 5 is an isometric exploded view of the embodiment of the insert asshown in FIG. 3.

FIG. 6 is a cross-sectional view of another embodiment of aself-adjusting liner assembly of the present invention prior to wear ofthe liner which includes a lubricating and cooling system.

FIG. 7 shows a sealing arrangement for a wear ring of the presentinvention.

FIG. 8 shows an embodiment of the sealing face of an impeller useful inthe present invention.

FIG. 9 is an isometric exploded view of another embodiment of aself-adjusting liner assembly of the present invention.

FIG. 10 a is a cross-sectional view of a portion of the self-adjustingliner assembly of FIG. 9 where the spring is fully contracted.

FIG. 10 b is a cross-sectional view of a portion of the self-adjustingliner assembly of FIG. 9 where the spring is fully expanded.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The detailed description set forth below in connection with the appendeddrawing is intended as a description of various embodiments of thepresent invention and is not intended to represent the only embodimentscontemplated by the inventor. The detailed description includes specificdetails for the purpose of providing a comprehensive understanding ofthe present invention. However, it will be apparent to those skilled inthe art that the present invention may be practiced without thesespecific details.

FIG. 1 is a cross-sectional view of a prior art conventional singlestage centrifugal pump 10. Centrifugal pump 10 comprises a stationarycasing (volute) 20 having a suction inlet 22 which is the point of entryof the slurry. Housed within the stationary casing 20 is an impeller 14and a shaft 12 for rotating the impeller 14. Typically, the shaft iscoupled to a motive power such as an electric motor (not shown).Impeller 14 has a gland side shroud 31 and a suction side shroud 32. Theimpeller vanes 24 are located in between the gland side shroud 31 andthe suction side shroud 32, and serve to accelerate the fluid towardsthe high-pressure region 28.

The slurry to be pumped enters the pump via suction inlet 22 (see arrows13) and is forced at high pressure through the rotating impeller 14 intothe high pressure region 28 inside the pump casing 20 from where it isdischarged via a discharge pipe (not shown). However, some of the slurrywill tend to flow from the high pressure region 28 back into the lowpressure region 30 in the suction inlet 22. Therefore, the suctionsurface 18 of impeller 14 typically wears more quickly than the glandsurface 16 due to the recirculation of the incoming slurry (see arrows11). Thus, a suction liner 26 is provided, which liner can be made froma variety of materials such as chrome white iron, elastomers and thelike, as is known in the industry. The suction liner 26 takes up some ofthe clearance at the suction side 18 of the impeller 14 to reducesuction side 18 recirculation and the possibility of abrasive solidsbeing trapped between the rotating impeller 14 and the casing 20 andsuction liner 26.

However, during use of the pump 10, both the suction liner 26 and theimpeller 14 wears and the space between the suction liner 26 and theimpeller 14 increases, leading to increased recirculation and eventuallythe pump 10 needs to be shut down so that both the suction liner 26 andthe impeller 14 can be replaced. It would be desirable to avoid thenumber of shut downs of the pump 10 which are necessary for replacingthe suction liner 26 and/or impeller 14. One way to accomplish thiswould be to provide a self-adjusting suction liner assembly which wouldadjust during operation to continuously ensure that the space betweenthe suction liner and the suction side of impeller is eliminated or keptat a minimum.

FIG. 2 shows one embodiment of a pump 110 which has been fitted with aself-adjusting suction liner assembly 180 of the present invention. Inthis embodiment, self-adjusting suction liner assembly 180 comprisessuction liner 126 having an insert 142, which insert 142 can be seenmore clearly in FIG. 5, and in the cross-sectional of self-adjustingsuction liner assembly 180 in FIG. 3. As can be seen in FIG. 2, thesubstantially planar outer most surface 160 of inset 142, whichcomprises wear ring 154, lies essentially flush with impeller 114 andtherefore prevents recirculation by blocking the flow of slurry (seearrows 115).

FIG. 4 is an isometric exploded view of the embodiment of theself-adjusting liner assembly 180 in FIG. 3. With reference now to FIGS.3 and 4, annular liner 126 has a recess 144 which houses insert 142.Insert 142 comprises annular gasket 146, an annular bottom cartridgeplate 148, annular wave spring 150, annular top cartridge plate 152 andannular wear ring 154. Wear ring 154 may be made from any wear resistantmaterial known in the industry such as urethane, elastomers, tungstencarbide, chrome white iron and the like, or a combination thereof.Choice of material will be driven by the need to reduce friction andabrasive wear. It is understood than any resilient, compressible membersuch as a coil/compression spring or the like could be used, however,wave springs are more desirable as they generally reduce the springheight by as much as 50% while still exerting the same force anddeflection as ordinary coil/compression springs. Each of annular gasket146, annular bottom cartridge plate 148, annular top cartridge plate 152and annular wear ring 154 further comprise a number of notches 162around their respective peripheries, which, when the insert 142 isassembled, line up and slide over anti-rotation keys 164 located in therecess 144 of annular liner 126 to ensure that insert 142 does notrotate during operation of the slurry pump.

In use, initially, the wave spring 150 is essentially fully compressedand forces the outer surface 160 of wear ring 154 to be essentiallyflush against the suction side of impeller 114, as shown in FIG. 2. Aswear ring 154 wears, however, the wave spring 150 continuously expandsto provide a constant force on the wear ring 154, which allows the outersurface 160 to be continuously flush against the impeller. Thus,recirculation is continuously reduced, resulting in longer wear life forthe pump parts. It is understood that the choice of annular spring,i.e., resilience member, will determine the forces desirable for thewear ring 154 on the suction side of impeller 114. Generally, excessivespring force is to be avoided, as this may result in excessive wear ofthe wear ring 154 and overheating due to excessive friction. Thus,generally, a relatively weak spring is desirable.

FIG. 6 describes an additional embodiment, where a fluid for lubricationand cooling is provided via multiple nozzles 290, which are fittedclosely to holes formed in the wear ring 254. The fluid is forcedthrough the wear ring by the aforementioned close fit, and enters asmall groove (not shown) created on the surface of the wear ring 254 forthe purpose of distributing the fluid along the full circumference ofthe wear ring. This groove may be extended, in a spiral or radialfashion, to the outer diameter of the wear ring 254, so that the coolingand lubricating fluid would tend to travel in that direction and carrycontaminants away from the continuous sealing surface between the groove291 and the inner diameter of the wear ring 254. The flow and pressureof the cooling and lubricating fluid would be monitored and controlledexternal to the pump, so it would be possible to find the minimumpressure required to overcome the spring pressure and create a thin filmof fluid between the wear ring 254 and the impeller sealing surface 18,which is likely to greatly reduce the wear rate of these two surfaces.

FIG. 7 describes the sealing arrangement 170 of the wear ring 154 in thegroove 144 created in the suction liner 126, the purpose of which istwofold. First, the seal must prevent flow from travelling from the highpressure region 28 to the low pressure region 30, along a pathunderneath the wear ring 154 and through the wave spring 150. Second,the seal must be located so that the fluid pressure at the outerdiameter of the wear ring 154 has equal access to both the sealing faceand the underside of the wear ring 154. This will prevent a net pressureimbalance on these two surfaces of the wear ring, which could result ina significant force that would overwhelm the wave spring. The sealshould be located at the inner diameter of the wear ring, and shouldallow for axial travel of the wear ring in the groove 144, whilemaintaining a seal. An o-ring, lip seal or similar arrangement may beappropriate.

FIG. 8 describes a possible embodiment of the sealing face of theimpeller 14, which may be lined with a material 200 other than chromewhite iron, such as tungsten carbide, polyurethane, or any othermaterial with desirable properties. Either the same or differentmaterials as those used in the wear ring 154 may be employed here. Thesealing face of the impeller 14 may be flush with the impeller surface18, or it may be recessed (as shown in FIG. 8), so as to create acircuitous path for any leakage across the sealing face.

FIG. 9 is an isometric exploded view of another embodiment of aself-adjusting liner assembly 280 of the present invention. In thisembodiment, annular liner 326 has a recess 344 which houses insert 342.Recess 344 comprises a number of holes 266 for receiving anti-rotationpins 368, to prevent rotation of the insert 342 during operation of theslurry pump. Insert 342 comprises an annular bottom steel plate 348, andannular top steel plate 352 and an annular spring 350 positionedtherebetween. Both the annular bottom steel plate 348 and the annulartop steel plate 352 further comprise a comparable number of holes 266 asthe recess 344 of the annular line 326 to also receive anti-rotationpins 368 to prevent rotation of the insert 342 during operation of thepump.

Insert 342 further comprises O-ring 368 for providing the proper sealingarrangement for assembly 380. Annular liner 326 comprises a groove 357for receiving O-ring 368. In this embodiment, wear ring 354 comprises arecess 355 for receiving steel plate 369. Generally, the wear ring ismade of rubber, polyurethane, and the like. The embedded steel ring 369provides structure to the wear ring 354, which wear ring can be made ofmore flexible, non-metallic materials. Furthermore, the embedded steelring 369 may comprise threaded holes (not shown) to receive screws forattaching the wear ring 354 and steel ring 369 to the annular top steelplate 352. The annular bottom steel plate 348 contains threaded holes toreceive screws for attaching the insert 342 to the annular liner 326.The assembly 380 is installed in the pump in the same manner as aregular annular liner with no self-adjusting insert 342 would be.

FIGS. 10 a and 10 b are partial cross-sectional views of the embodimentof the self-adjusting liner assembly 380 shown in FIG. 9. FIG. 10 ashows the annular spring 350 of insert 342 in its full contracted stateand FIG. 10 b shows the annular spring 350 of insert 342 in its fullyexpanded state.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions. Thus, the present invention is not intended to be limited tothe embodiments shown herein, but is to be accorded the full scopeconsistent with the claims, wherein reference to an element in thesingular, such as by use of the article “a” or “an” is not intended tomean “one and only one” unless specifically so stated, but rather “oneor more”. All structural and functional equivalents to the elements ofthe various embodiments described throughout the disclosure that areknown or later come to be known to those of ordinary skill in the artare intended to be encompassed by the elements of the claims. Moreover,nothing disclosed herein is intended to be dedicated to the publicregardless of whether such disclosure is explicitly recited in theclaims.

We claim:
 1. A self-adjusting liner assembly for installation within a centrifugal pump of the type having an impeller and a pump casing having a suction inlet, comprising: a liner having a sealing end, the sealing end having at least one substantially planar outer most surface for contacting an outer surface of the impeller; and a resilient member disposed in the liner, said resilient member providing a force so that the at least one outer most surface remains in substantially continuous contact with the outer surface of the impeller.
 2. The self-adjusting liner assembly as claimed in claim 1, wherein the at least one outer most surface comprises a wear ring.
 3. The self-adjusting liner assembly as claimed in claim 1, wherein resilient member is a spring.
 4. The self-adjusting liner assembly as claimed in claim 3, wherein the spring is a wave spring.
 5. The self-adjusting liner assembly as claimed in claim 2, wherein the liner includes a recessed portion for housing the resilient member and the wear ring.
 6. The self-adjusting liner assembly as claimed in claim 1, wherein the liner is formed from a wear resistant iron such as chrome white iron.
 7. The self-adjusting liner assembly as claimed in claim 2, wherein the wear ring is made from a material selected from the group consisting of urethane, tungsten carbide and chrome white iron.
 8. The self-adjusting liner assembly as claimed in claim 1, further comprising a lubricating and cooling system for providing water to the at least one substantially planar outer most surface.
 9. A self-adjusting liner assembly for installation within a centrifugal pump of the type having an impeller and a pump casing having a suction inlet, comprising: a liner having a sealing end, the sealing end having a substantially planar outer most surface comprising a wear ring for contacting an outer surface of the impeller; and a resilient member disposed in the liner, said resilient member providing a force so that the wear ring of the outer most surface remains in substantially continuous contact with the outer surface of the impeller.
 10. The self-adjusting liner assembly as claimed in claim 9, wherein resilient member is a spring.
 11. The self-adjusting liner assembly as claimed in claim 10, wherein the spring is a wave spring.
 12. The self-adjusting liner assembly as claimed in claim 9, wherein the liner includes a recessed portion for housing the resilient member and the wear ring.
 13. The self-adjusting liner assembly as claimed in claim 9, wherein the liner is formed from a wear resistant iron such as chrome white iron.
 14. The self-adjusting liner assembly as claimed in claim 9, wherein the wear ring is made from a material selected from the group consisting of urethane, tungsten carbide and chrome white iron.
 15. The self-adjusting liner assembly as claimed in claim 9, further comprising a lubricating and cooling system for providing water to the at least one substantially planar outer most surface. 